Catheters are increasingly used to access remote regions of the human body and, in doing so, delivering diagnostic or therapeutic agents to those sites. In particular, catheters which use the circulatory system as the pathway to these treatment sites are especially practical. Catheters are also used to access other regions of the body, e.g., genito-urinary regions, for a variety of therapeutic and diagnostic reasons.
Often the target which one desires to access by catheter is within a soft tissue such as the liver or the brain. These are difficult sites to reach. The catheter must be introduced through a large artery such as those found in the groin or in the neck and then be passed through ever-narrower regions of the arterial system until the catheter reaches the selected site. Often such pathways will wind back upon themselves in a multi-looped path. These catheters are difficult to design and to utilize since they must be fairly stiff at their proximal end so to allow pushing and manipulation of the catheter as it progresses through the body, and yet must be sufficiently flexible at the distal end to allow passage of the catheter tip through the loops and increasingly smaller blood vessels mentioned above and yet at the same time not cause significant trauma to the blood vessel or to the surrounding tissue. Further details on the problems and an early, but yet effective, way of designing a catheter for such a traversal may be found in U.S. Pat. No. 4,739,768, to Engelson.
These catheters are designed to be used with a guidewire. A guidewire is simply a wire, typically of very sophisticated design, which is the "scout" for the catheter. The catheter fits over and slides along the guidewire as it passes through the vasculature. Said another way, the guidewire is used to select the proper path through the vasculature with the urging of the attending physician and the catheter slides along behind once the proper path is established.
The human vasculature is quite complex. It is believed that each person's vasculature is unique and indeed could be used as an identifying characteristic of an individual. Be that as it may, there are a few times when, irrespective of the fine design of a guidewire and enhanced trackability of a specific catheter may not in combination allow access to a specific site in the human body. Multiple turns through a neurological area or decreasing radius arterial turns may require that the catheter be slightly modified. It is common practice that suppliers of neurovascular catheters provide mandrels so that the distal end of such catheters be shaped using steam or the like prior to introduction into the human body Because of the inherent flexibility of such neurovascular catheters, the modest shaping imparted to the distal tip of the catheter is usually easily straightened by a more substantial region of the guidewire.
The catheter section at hand, of necessity, includes a tubular forming member containing at least some amount of super-elastic alloy. Consequently, it is quite difficult to form these distal tips in an operating theater. It is therefore desirable that some provision be made for providing a shaping function to such supported catheter sections. In this invention, the metallic forming member is; provided with a shape using a heat treatment step and the polymeric material surrounding the catheter is then used to hold the thusly-shaped forming member in another shape. For instance, a crooked or bent shape may be provided to the forming member during the heat treatment step. The overlying polymeric sheath is then used to straighten the forming member and hold it in a non-equilibrium condition. The polymeric material in the outer layer is then heated using, e.g., steam, and the material in the forming member pulls the shape of the catheter assembly over into a form approximating that given the forming member during the heat treatment step. Ideally, the physician is able to use one or the other of the two shapes for the particular involved situation. It is within the ambit of this invention that only a portion of the affected region of the catheter section be heated so to provide some intermediate shape between the first shape and the second heated shape.
This invention is an adaptable one and may be used in a variety of catheter formats. The invention utilizes the concept of combining one or more polymeric tubes with a metallic tubular forming member comprising a super-elastic alloy. The construction technique has the benefit of producing catheter sections having small overall diameters but with exceptional strength, resistance to kinking, and recovery from kinking (even in vivo) should such kinking occur. It may be used with the distal tip either in the first shape or in the post-heated second shape or in any transitional shape between. This catheter may be used in conjunction with a guidewire, but the catheter body may also be used as a flow-directed catheter with the attachment of a balloon or in combination with a specifically flexible tip, as is seen, for instance, in U.S. Pat. No. 5,336,205 to Zenzen et al., the entirety of which is incorporated by reference.
The use of a stiffening section in a catheter body is not a novel concept. Typical background patents are discussed below. However, none of these documents have used our concept to produce a catheter section with the forming capabilities of this invention.
Multi-Wrap Catheters
There are a number of catheters discussed in the literature which utilize catheter bodies having multiply-wrapped reinforcing material. These catheters include structures having braided bands or ones in which the spirally wound material is simply wound in one direction and the following layer or layers are wound in the other.
Krippendorf, U.S. Pat. No. 2,437,542, describes a "catheter-type instrument" which is typically used as a ureteral or urethral catheter. The physical design is said to be one having a distal section of greater flexibility and a proximal section of lesser flexibility. The device is made of intertwined threads of silk, cotton, or some synthetic fiber. It is made by impregnating a fabric-based tube with a stiffening medium which renders the tube stiff yet flexible. The thus-plasticized tubing is then dipped in some other medium to allow the formation of a flexible varnish-like layer. This latter material may be a tung oil base or a phenolic resin and a suitable plasticizer.
Similarly, U.S. Pat. No. 3,416,531, to Edwards, shows a catheter having braiding-edge walls. The device further has additional layers of other polymers such as TEFLON and the like. The strands found in the braiding in the walls appear to be threads having circular cross-sections. There is no suggestion of constructing a device using ribbon materials. Furthermore, the device is shown to be fairly stiff in that it is designed so that it may be bent using a fairly large handle at its proximal end.
U.S. Pat. No. 3,924,632, to Cook, shows a catheter body utilizing fiberglass bands wrapped spirally for the length of the catheter. As is shown in FIG. 2 and the explanation of the Figure at column 3, lines 12 and following, the catheter uses fiberglass bands which are braided, that is to say, bands which are spiraled in one direction cross over and under bands which are spiraled in the opposite direction. Additionally, it should be observed that FIG. 3 depicts a catheter shaft having both an inner lining or core 30 and an outer tube 35.
U.S. Pat. No. 4,425,919, to Alston, Jr. et al., shows a multi-layered catheter assembly using multi-stranded flat wire braid. The braid 14 in FIG. 3 further covers an interior tubing or substrate 12.
U.S. Pat. No. 4,484,586 shows a method for the production of a hollow, conductive medical tubing. The conductive wires are placed in the walls of hollow tubing specifically for implantation in the human body, particularly for pacemaker leads. The tubing is preferably made of an annealed copper wire which has been coated with a body-compatible polymer such as a polyurethane or a silicone. After coating, the copper wire is wound into a tube. The wound substrate is then coated with still another polymer to produce a tubing having spiral conducting wires in its wall.
A document showing the use of a helically wound ribbon of flexible material in a catheter is U.S. Pat. No. 4,516,972, to Samson. This device is a guiding catheter and it may be produced from one or more wound ribbons. The preferred ribbon is a polyaramid material known as Kevlar 49. Again, this device is a device which must be fairly stiff. It is a device which is designed to take a "set" and remain in a particular configuration as another catheter is passed through it. It must be soft enough so as not to cause substantial trauma, but it is certainly not for use with a guidewire. It would not meet the flexibility criteria required of the inventive catheter described herein.
U.S. Pat. No. 4,806,182, to Rydell et al, shows a device using a stainless steel braid imbedded in its wall and having an inner layer of a polyfluorocarbon. The process also described therein is a way to laminate the polyfluorocarbon to a polyurethane inner layer so as to prevent delamination.
U.S. Pat. No. 4,832,681, to Lenck, shows a method and apparatus useful for artificial fertilization. The device itself is a long portion of tubing which, depending upon its specific materials of construction, may be made somewhat stiffer by the addition of a spiral reinforcement comprising stainless steel wire.
U.S. Pat. No. 4,981,478, to Evard et al., discloses a multi-sectioned or composite vascular catheter. The interior section of the catheter appears to have three sections making up the shaft. The most interior (and distal) section, 47, appears to be a pair of coils 13 and 24 having a polymeric tubing member 21 placed within it. The next, more proximal, section is 41, and FIG. 4 shows it loo be "wrapped or braided" about the next inner layer discussed just above. The drawing does not show it to be braided but, instead, a series of spirally wrapped individual strands. Finally, the outermost tubular section of this catheter core is another fiber layer 49, of similar construction to the middle section 26 discussed just above.
Another catheter showing the use of braided wire is shown in U.S. Pat. No. 5,037,404, to Gold et al. Mention is made in Gold et al of the concept of varying the pitch angle between wound strands so to result in a device having differing flexibilities at differing portions of the device. The differing flexibilities are caused by the difference in pitch angle. No mention is made of the use of ribbon, nor is any specific mention made of the particular uses to which the Gold et al. device may be placed.
U.S. Pat. No. 5,057,092, to Webster, Jr., shows a catheter device used to monitor cardiovascular electrical activity or to electrically stimulate the heart. The catheter uses braided helical members having a high modulus of elasticity, e.g., stainless steel. The braid is a fairly complicated, multi-component pattern shown very well in FIG. 2.
U.S. Pat. No. 5,176,660 shows the production of catheters having reinforcing strands in their sheath wall. The metallic strands are would throughout the tubular sheath in a helical crossing pattern so to produce a substantially stronger sheath. The reinforcing filaments are used to increase the longitudinal stiffness of the catheter for good "pushability". The device appears to be quite strong and is wound at a tension of about 250,000 lb./in..sup.2 or more. The flat strands themselves are said to have a width of between 0.006 and 0.020 inches and a thickness of 0.0015 and 0.004 inches.
Another variation which utilizes a catheter wall having helically placed liquid crystal fibrils is found in U.S. Pat. No. 5,248,305, to Zdrahala. The catheter body is extruded through an annular die, having relatively rotating inner and outer mandrel dies. In this way, the tube containing the liquid crystal polymer plastic-containing material exhibits a bit of circumferential orientation due to the rotating die parts. At column 2, line 40 and following, the patent suggests that the rotation rate of the inner and outer walls of the die may be varied as the tube is extruded, with the result that various sections of the extruded tube exhibit differing stiffnesses.
U.S. Pat. No. 5,217,482 shows a balloon catheter having a stainless steel hypotube catheter shaft and a distal balloon. Certain sections of the device shown in the patent use a spiral ribbon of stainless steel secured to the outer sleeve by a suitable adhesive to act as a transition section from a section of very high stiffness to a section of comparatively low stiffness.
Japanese Kokai 05-220,225, owned by the Terumo Corporation, describes a catheter in which the torsional rigidity of the main body is varied by incorporating onto an inner tubular section 33, a wire layer which is tightly knitted at the proximal section of the catheter and more loosely knitted at a midsection.
Single-Layer, Reinforced Catheters
There are a variety of catheters which, unlike the devices discussed above, utilize but a single layer of reinforcing material.
For instance, U.S. Pat. No. 243,396 to Pfarre, patented in June of 1881, shows the use of a surgical tube having a wire helix situated within the tube wall. The wire helix is said to be vulcanized into the cover of the device.
U.S. Pat. No. 2,211,975, to Hendrickson, shows a similar device also comprising a stainless steel wire 15 embedded in the inner wall of a rubber catheter.
U.S. Pat. No. 3,757,768, to de Toledo, shows a "unitary, combined spring guide-catheter that includes an inner wall portion formed as a continuous helical spring with the helices in contact with each other and an outer wall portion formed from an inert plastic material enclosing the spring in such a manner as to become firmly bonded to the spring while having its outer surface smooth". There is no suggestion to separate the windings of the coil in any fashion.
U.S. Pat. No. 4,430,083 describes a catheter used for percutaneous administration of a thrombolytic agent directly to a clot in a coronary artery. The device itself is an elongated, flexible tube supported by helically wound wire having a specific cross-sectional shape. The wire is wound into a series of tight, contiguous coils to allow heat shrinking of tubing onto the outside of the wire of the shape of the outer surface of the wire as wound into the helix provides tile heat-shrunk tubing with footing for a tight fit.
U.S. Pat. No. 4,657,024, to Coneys, shows a catheter which employs a set of helical strips within the wall of the catheter. However, the helical strips are of a radio-opaque material, e.g., fluorinated ethylene-propylene. It is not clear that the blended radio-opaque material necessarily provides any physical benefit other than the ability to allow the catheter shaft to be seen when viewed with a fluoroscope.
U.S. Pat. No. 4,737,153, to Shimamura et al., describes a device which is characterized as a "reinforced therapeutic tube" and which uses a spiral reinforcing material embedded within the wall of the device.
U.S. Pat. No. 5,069,674, to Fearnot et al. (and its parent, U.S. Pat. No. 4,985,022), shows a small diameter epidural catheter having a distal tip made up of a stainless steel wire which is helically wound and placed within a tubular sheath or tube.
Similarly, U.S. Pat. No. 5,178,158, to de Toledo, shows what is characterized as a "convertible wire for use as a guidewire or catheter". The patent describes a structure which comprises an interior wire or spring section shown, in the drawings, to be of generally rectangular cross-section. Outer layers of the device include a polyamide sheath placed adjacent to the helical coil at the proximal end of the catheter (see column 4, lines 64 and following). The device also comprises an outer sheath 40 of Teflon that extends from the proximal end 12 to the distal end 14 of the device. The overlying sheath 40 may extend or overhang at the proximal or the distal end of the catheter. The distal tip portion 13 is said to be "flexible, soft, and floppy". The PCT Published Application corresponding to this patent is WO 92/07507.
U.S. Pat. No. 5,184,627 shows a guidewire suitable for infusion of medicaments to various sites along the guidewire. The guidewire is made up of a helically wound coil having a polyamide sheath enclosing its proximal portion and a Teflon sheath tightly covering the entire wire coil. The coil is closed at its distal end.
U.S. Pat. No. 5,313,967, to Lieber et al., shows a medical device, a portion of which is a helical coil which apparently may include an outer plastic sheath in some variations. Apparently, a secondary helix of a somewhat similar design (in that it is formed by rotating a flat wire or the like along its longitudinal axis to form a screw-like configuration) is included within the helical coil to provide axial pushability and torque transmission.
U.S. Pat. No. 5,405,338, to Kranys, describes a helically wound catheter incorporating a shaft component having a helically wound coil with a skin or webbing supported by the coil. The skin or webbing is said to contribute "negligibly to the resistance of the catheter to axially directed compressive forces. . ." The catheter may include an inner, taut skin component.
The PCT application, WO 93/15785, to Sutton et al., describes kink-resistant tubing made up of a thin layer of an encapsulating material and a reinforcing coil. As is shown in the drawings, the supporting material is embedded within the wall of the tubing in each instance.
The PCT application bearing the number WO 93/05842, to Shin et al., shows a ribbon-wrapped catheter. The device is shown as a section of a dilatation catheter. The inner section 34 is a helically wound coil and is preferably a flat wire. See, page 6, lines 25 and following. The coil is then wrapped with a heat-shrunk jacket 34 formed of low-density polyethylene. A lubricious material such as a silicone coating may then be placed on the inner surface of the spring coil to "enhance handling of the guidewire". It is also said, on page 6 of the document, that the "entire spring coil, before it is wound or jacketed, may be coated with other materials such as Teflon to enhance lubricity or provide other advantages. In some embodiments, the spring coil has been plated with gold."
Endoscope Structures
Various endoscopic structures, used primarily in sizes which are larger than endovascular catheters utilize structures including stiffener materials.
U.S. Pat. No. 4,676,229, to Krasnicki et al., describes an endoscopic structure 30 having an ultra-thin walled tubular substrate 31 formed of a lubricious material such as TEFLON. The structure contains a filament supported substrate. The filament is coated with and embedded into a filler material, typically an elastomeric material. A highly lubricious outer coating 35, all as shown in FIG. 2, forms the outer layer of the device. FIG. 3 in Krasnicki et al., describes another variation of the endoscopic device in which a different selection of polymer tubing is utilized but the placement of the filamentary support remains varied in an intermediate material of an elastomer. In some variations of the device, the filament is strongly bonded to the inner tubular substrate using an adhesive 37 "such as an epoxy cement having sufficient bond strength to hold the :filament to the substrate as it is deformed into a tight radius." See, column 3, lines 50 and following.
U.S. Pat. No. 4,899,787, to Ouchi et al. (and its foreign relative, German Offenlegungschrift DE-3242449) describes a flexible tube for use in an endoscope having a flexible, basic tubular core structure made up of three parts. The three parts are an outer meshwork tube, an intermediate thermoplastic resin tube bonded to the outer meshwork tube, and an inner ribbon made of a stainless steel or the like which is adherent to the two polymeric and meshwork tubes such that the resin tube maintains an adherent compressive pressure in the finished flexible tube. The patent also suggests the production of an endoscope tube having "flexibility which varies in step-wise manner from one end of the tube to the other . . . [and is produced] by integrally bonding two or more thermoplastic resin tube sections formed of respective resin materials having different hardnesses to the outer surface of the tubular core structure . . .". See, column 2, lines 48 and following.
U.S. Pat. No. 5,180,376 describes an introducer sheath utilizing a thin, flat wire metal coil surrounded only on its exterior surface with a plastic tube of coating. The flat wire coil is placed there to lower the "resistance of the sheath to buckling while minimizing the wall thickness of the sheath." A variation using two counterwound metal ribbons is also described.
European Patent Application 0,098,100 describes a flexible tube for an endoscope which uses a helically wound metallic strip having a braided covering contiguous to the outer surface of the coil and having still further out a polymeric coating 9. Interior to the coil is a pair of slender flexible sheaths which are secured to a "front-end piece 10" by soldering.
Japanese Kokai 2-283,346, describes a flexible endoscope tube. The tubular outer shell is made up of two layers of a high molecular weight laminated material. The tube also has an inner layer of an elastic material and interior to it all is a metallic ribbon providing stiffening.
Japanese Kokai 03-023830, also shows the skin for flexible tube used in an endoscope which is made up of a braid 3 prepared by knitting a fine wire of a metal with a flexible portion 2 which is prepared by spirally winding an elastic belt sheet-like material and a skin 4 with which the whole outer surface of the device is covered. The document appears to emphasize the use of a particular polyester elastomer.
Japanese Kokai 5-56,910, appears to show a multi-layered endoscope tube made up of layers of the spiral wound metallic ribbon covered by a polymeric sheath.
French Patent Document 2,613,231, describes a mrledical probe used with an endoscope or for some other device used to stimulate the heart. The device appears to be a helix having a spacing between 0 and 0.25mm (See page 4, line 20) preferably rectangular in cross section (See Page 4, Line 1) and of a multi-phase alloy such as M35N, SYNTACOBEN, or ELGELOY (See Page 4).
German Offenlegungschrift DE-3642107 describes an endoscope tube, formed of a spiral tube, a braid formed of fibers interwoven into a net (which braid is fitted on the outer peripheral surface of the spiral tube), and a sheath covering the outer peripheral surface of the braid.
None of the noted devices appear to have a distal tip which changes from a first desired shape to a second desired shape upon application of heat and remain in that second shape.